In a known producing method for a nonwoven fabric, numerous filaments ejected from a spinning nozzle are drawn by an air gun and are stretched. Then, the filaments are carried by an air flow into a guide tube, and are dispersed in a dispersing device (usually formed as a dispersing nozzle or a dispersing pipe). Then, the filaments are collected on a moving collector surface to thereby form a web.
In Japanese Patent Publication No. 47-24991, there is described a device for dispersing and depositing filaments to produce a fleece (a kind of web). As a dispersing portion of this device, there are shown in the above reference an example wherein a space w between opposed side plates (corresponding to side walls) of a dispersing pipe and a space t between opposed dispersing plates (facing parts of the dispersing pipe other than the opposed side plates) are linearly changed (FIG. 1 in the above reference); an example wherein the space w between the opposed side plates is increased toward an outlet (filaments outlet) of the dispersing pipe in such a manner that a radius of curvature of the opposed side plates is gradually decreased toward the outlet (FIG. 2(a) in the above reference); and an example wherein the space w between the opposed side plates is linearly increased along tangential lines of arcs and the arcs are connected with expanded ends of the tangential lines (FIG. 2(b) in the above reference).
However, in the dispersing device formed as the dispersing pipe as described in Japanese Patent Publication No. 47-24991, a change in sectional area of the device is large, or the space w between the opposed side plates is rapidly increased toward the filaments outlet. Accordingly, the air flow in the device separates from the opposed side plates and the opposed dispersing plates, causing remarkable turbulence of the air flow. As a result, the filaments carried by the air flow are largely disturbed to cause the generation of yarn bundles damaging the appearance of the web.